1. Field of the Invention
The present invention relates generally to hydrodynamics of droplet formation and, more particularly, to a printhead design that enhances performance of thermal ink-jet pens.
2. Description of the Related Art
The art of thermal ink-jet (TIJ) printhead fabrication is relatively well developed. The basics are disclosed, for example, in some detail in the Hewlet-Packard Journal, Vol. 36, No. 5, May 1985, incorporated herein by reference.
In the field of TIJ printing, it is known to provide a printhead having an orifice plate in combination with heating elements such that thermal excitation of ink is used to eject droplets through tiny nozzles onto a print media. The orifice plate configuration is one of the design factors that controls droplet size, velocity and trajectory.
In the prior art, it is known to align printhead orifice plate nozzles with underlying heating elements as shown in FIGS. 1 and 2. Heat from an element 2 causes a vapor bubble to grow rapidly in an ink channel 4 and gives momentum to the ink above the bubble. The ink in turn is propelled through a nozzle 6 in an orifice plate 8 and onto the print media.
One of the problems associated with TIJ printing is obtaining repeatability of the ejected ink droplet size. In general, a droplet volume will have deviation of about four to eight percent in such a design arrangement as shown in the FIGURES.
Hence, there is a need to improve repeatability of ink droplet volume in order to improve print quality and uniformity.